I think we are talking about two related issues here: grain or grain-free and high carb or low carb formulas.
Some people feed grain-free because they believe their dog has an intolerance or allergy to most grains. The formula they chose may be grain-free and high carb like Natural Balance Sweet Potato and Fish (21% protein, 10% fat and about 50% carbohydrates) or grain-free and low carb like EVO (42% protein, 22% fat and 12% carbs).
Other people feed grain-free kibble because they believe low carb diets are healthier for dogs and the grain-free kibbles with moderate to high proteins like EVO, Orijen, Wellness Core, Acana Prairie Harvest, Horizon Legacy, etc. are the one way to get a low carb formula. Theoretically, a kibble could be higher protein and low carb and still use a grain like millet or oatmeal, but the dog food companies haven't seen that as a marketing route and don't make them.
Grains, in and of themselves, don't make a food high or low in carbs, protein, etc. It's the percentage of meat protein and fats primarily that determine the carb percentage. To figure the carbohydrate percentage somewhat accurately for a kibble:
Start with 100%. Subtract the listed percentages of protein, fat, moisture, and ash (often not listed but usually 5-10%). The remainder is the carbohydrate percentage.
My senior Bentley has eaten a rotation of moderate to high protein grain-free formulas for the last 3 years. They have been the healthiest years of his life in terms of energy level, coat and skin condition, and reduction of yeasty ears. When I first transitioned him to low carb and grain-free, it took a little while to adjust because he was so used to the other kind of kibble. My 2 year old lab has only ever been fed low-carb grain free. I've used Orijen, EVO, Acana Prairie Harvest and just started Horizon Legacy. Wellness Core seemed to cause itchiness in my lab so I discontinued it.
